There are many different material handling systems consisting of conveyor systems and conveyor installations including more or less intelligent control for handling and transporting goods, e.g. workpieces, between different work positions in the manufacture of goods that require several work steps. In one type of material handling system, the conveyor system consists of a main conveyor, which in turn can consist of a plurality of conveyor belts, and a plurality of side conveyors. A side conveyor selectively leads workpieces from the main conveyor to work stations where one or more work steps are performed on the workpiece, after which the workpiece is returned to the main conveyor with the aid of the side conveyor.
A particular type of material handling system comprises a conveyor system in which the main conveyor is placed above the work positions. The workpieces are here secured on hanging product carriers, which are moved on the main conveyor, which can comprise an endless conveyor belt. The side conveyors in this case consist of work stations which are adapted to selectively move a product carrier from the main conveyor, which is located at an upper level, down to a work position, which is located at a lower level, with the aid of a conveyor chain. When the work step has been carried out, the conveyor chain transports the product carrier with the workpiece up to the main conveyor again for continued transport of the product carrier to the next work station. Each product carrier comprises a product holder in which one or more workpieces are secured. The product holder is adapted to the product that is being manufactured and can hold one or more workpieces. These can be, for example, parts of a shirt, in which case the product holder holds all the parts of a shirt at the start of the transport flow and in which the product holder only holds the finished shirt when the product carrier reaches the end of the transport flow. Each product carrier can also comprise some form of identification means, such that the product carrier can be identified by the system, which means that each product carrier can be conveyed to predetermined work stations and onward to predetermined work positions. Such material handling systems are known to a person skilled in the art and are common particularly in the clothing industry.
The conveyor chain that conveys the product carriers in a work station, from the main conveyor to the work position, consists of a number of articulated links, which can be carrier links and intermediate links. A carrier link can also be referred to as an inner link, and an intermediate link can also be referred to as an outer link. Each conveyor chain is driven by one or more separately controlled chain wheels. The carrier links are adapted to be able to couple to and secure a product carrier for transporting workpieces to the work position and for transporting the product carrier back to the main conveyor after the work step has been carried out. The product carrier enters the conveyor chain at a loading position and is securely held by a carrier link until the product carrier is released at a release position at the main conveyor. The product carrier is preferably stopped at the work position when the work step is being carried out, without the product carrier having to be detached from the conveyor chain. If necessary, a product carrier can be released from the conveyor chain, for example for maintenance.
For the product carrier to be coupled to and uncoupled from the conveyor chain, a carrier link is designed with a retaining device in the form of a chain lock which can be opened for receiving a product carrier and closed in order to retain the product carrier. The chain lock can be opened in different ways, for example by a lever arm or by a specially adapted chain wheel. A known carrier link, described in U.S. Pat. No. 4,817,778 A1, is provided with a spring-loaded chain lock, which is opened each time it passes an opening chain wheel, and which closes, via the spring, when it leaves the opening chain wheel. The conveyor chain is driven by a drive chain wheel positioned at the loading position. A further chain wheel which is not driven is positioned at the release position. In this way, the conveyor chain hangs freely between the loading position and the release position and is pulled by the drive chain wheel from the upper chain wheel to the drive chain wheel. The conveyor chain may be supported by a slide support between the release position and the loading position.
Since the conveyor chain is driven by the drive chain wheel at the loading position, the conveyor chain can hang freely such that the lowermost position of the conveyor chain will be situated at the work position at the work station. When a product carrier reaches the work position, the operation on the workpiece can be performed and the product carrier continuous to the release position.
In another work station, described e.g. in CN 101766353 A, the drive motor drives the upper chain wheel, at the release position for the product carrier. The work station also comprises a chain wheel at the loading position. In such a work station, it is necessary to use an extra chain wheel at the lowermost position of the conveyor chain, in order to stabilize the conveyor chain since the conveyor chain cannot hang freely when the upper chain wheel drives the conveyor chain.
Both the described work stations functions properly. There is however room for an improved work station.